Rare earth materials are widely used, in addition to cell phones, TV screens, stereos, and energy-saving light bulbs, which are closely related to our lives, they are also important materials for the production of many high-tech products, such as electric cars, magnetic levitation trains, the nuclear energy industry, and superconductors, and so forth, all of which are essential. Therefore, rare earths play an important role in the materials industry.
●Recognizing Rare Earths
Rare earth element (REE) is also known as rare earth metal. It is composed of scandium, yttrium and lanthanide of group III of the periodic table, and contains a total of 17 elements. The special feature of rare earth is that its elements have special electronic structure, strong chemical activity, and large atomic radius, so they have the following excellent modification potential for general metals and alloys:
1. Metamorphism: After adding rare earth elements to the alloy, the microstructure will be significantly refined.
II, purification effect: rare earth element activity, and there is crystal surface adsorption, so often interact with impurity elements in the metal to generate stable compounds distributed on the grain boundary, thereby reducing the impurity content of the solid solution to improve the mechanical and physical properties of the metal.
*Solid solution refers to the alloy phase in which solute atoms are dissolved into the solvent lattice while still retaining the solvent type.
III.Strengthening effect: there is a certain solid solubility in the metal. In the solid solubility of small iron, cobalt, nickel and other metals for the alloying effect, and then at the same time the grain boundaries of the polymerization inhibit grain growth, improve the metal and alloy deformation resistance and fracture resistance.
*Solid solubility:The concentration of solute in a saturatedsolid solutionformed by solid solution of solute in solvent.
*Grain growth is actually just a displacement process of grain boundaries
IV. Improvement of high-temperature mechanical properties: refinement of the alloy organization, but also to prevent the growth of grain size during the heating process, which can improve the high-temperature fracture resistance of metallic alloys.
V. Resistance to high temperature corrosion and oxidation resistance: rare earth to improve the structure of the oxide mill, improve the adhesion of the oxide film and the substrate, not easy to peel off good protection, significantly improve the oxidizing properties.
VI.Surface modification: It can increase the penetration speed and penetration thickness of the surface treatment of metal components, reduce the total penetration temperature, save energy, and improve the anti-abrasion and anti-corrosion properties of the surface penetration layer.
●Application of Rare Earth Materials
1. Rare earth polishing materials: the polishing of rare earth in glass devices is mainly based on CeO2. The new cerium oxide-based rare earth polishing powder is mainly used in liquid crystal displays, integrated glass, storage discs, precision optical glass, etc.
2. Rare earth magnetic materials: neodymium, neodymium, praseodymium, dysprosium, etc. are the main raw materials for the manufacture of modern super permanent magnet materials, and their magnetic properties are 4-10 times higher than ordinary permanent magnet materials, and are widely used in high-tech fields such as television, audio, medical equipment, maglev trains and military industry. Rare earth cobalt and NdFeB permanent magnet materials have excellent characteristics of magnetic materials and are widely used in the electronics and aerospace industries.
3. Rare earth catalysts/catalytic materials: In addition to being used to make petroleum cracking catalysts, they are also widely used in many chemical reactions. Rare earths are also used in automobile exhaust gas purification to improve the mechanical strength of the catalyst carrier, convert toxic CO into CO2, and improve catalyst activity.
4. Rare earth storage light materials: MMNi5 (MM is a mixed rare earth metal) and LaNi5, compounds of rare earth and transition element nickel, are excellent hydrogen absorbing materials, known as “hydrogen sponges”. (The Dutch company Philips has found that LaNi5 has excellent hydrogen storage performance, that is, energy storage performance.) The theoretical capacity is up to 372Watt-hr/kg. It has heating hydrogen absorption; The characteristics of cooling and hydrogen release, the chemical formula of action is as follows: LaNi5+3H2 →LaNi5H6)
5. Rare earth luminescent/optical materials: Due to the special electronic structure layer of rare earth elements, they have abundant electronic energy levels and luminescent excited states, which can produce abundant radiation absorption and emission, covering almost the range from ultraviolet to visible red light. Therefore, it is widely used in information display, medical treatment, lighting, high-energy particle detection and recording, optoelectronic communication, military and other fields.
6. Rare earth superconducting materials: have the characteristics of zero resistance and complete diamagnetism. The superconducting material made of yttrium-barium-copper oxide improved by yttrium-barium copper oxide can obtain superconductors in the temperature region< of liquid nitrogen at -196 °C (<77 K°), making a great breakthrough in superconductor materials.
7. Metallurgical industry: The amount of rare earth used in the metallurgical industry is very large, accounting for 1/3 of the total amount. Rare earth elements are easy to form oxides, sulfides and sulfur oxides with high melting points and low plasticity at high temperatures with oxygen and sulfur. Adding rare earth to molten steel can play a role in desulfurization and deoxidation, improve the toughness of steel at normal and low temperatures, reduce the thermal brittleness of some steels, and improve the firmness of machinability weldments.
8. National defense applications: rare earths play an important role in roads, seas, air, information and telecommunications forces, such as: used in armor steel, artillery structural parts, tank laser ranging, spacecraft structural parts, and electronic jamming warfare traveling wave tubes, etc.
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